Consider an experiment in which an Hfr strain of E. coli bacteria with the StrS, his , met alleles in its genome is mixed with an F- strain of E. coli with the StrR, his-, and met- alleles in its genome. After the cells have been cultured together for 8 hours, the mixture of cells is plated on minimal media containing Streptomycin. Which genotype do you expect to be most common among the colonies that grow

F-: StrR, his+ and met+

Explanation:

the strain Hfr is a high-frequency strain of recombination that includes the F plasmid (fertility factor). Therefore, the whole genome sequence is able to be passed via Hfr to its receiver, but it needs a long duration of physical contact with the recipient because the recipient gets a gene (long time physical contact is seldom attained) and retains the F strain. Also, genomes from the F-cells are not passed backwards to the HF cells. Therefore, only F strain with tolerance to Streptomycin and capable of synthesizing its amino acids on limited media can thrive in this situation. Which is F-: StrR, his+ and met+ recombining.

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